Interface structures in Al-Nb2O5 nanocomposites processed by high-pressure torsion at room temperature

Abstract

Extremely thin Nb2O5 nanowires and Al powder were successfully consolidated at room temperature by using high-pressure torsion (HPT), producing a novel metal matrix nanocomposite with exceptional mechanical properties. It is shown that minor additions of Nb2O5 increase sharply the hardness of commercially pure Al. For instance, hardness of over 180 Hv was developed at the edge of samples with 10% nanowires and processed through 10 turns of HPT. This is markedly higher than any other value reported for pure aluminum matrix composites having this level of reinforcement phase. A detailed characterization of the interface structure using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) revealed a pronounced grain refinement of the Al matrix at the nanoscale and the occurrence of the aluminothermic reduction of the part of Nb2O5. The latter led to: (i) the formation of Al2O3 nanolayer at the Al/Nb2O5 interface and (ii) the nanosegregation of metallic Nb (with few atomic layers) along grain boundaries and dislocations. The pronounced increase in hardness is attributed to the formation of this interface nanostructure.